The invention proceeds from a radial piston machine whose pistons are subjected on the inside to pressure and are in each case supported on the lifting ring via a roller held axially on the end sides by roller guides.
The publication GB 2 238 086 B discloses a radial piston machine which has these features and for which the outlay on manufacturing techniques, associated up to now with the axial positioning of the rollers, and therefore the manufacturing and assembly costs are intended to be reduced. This object is intended to be achieved by the fact that a wedge-shaped piece having a circular-segment-like cross section, as viewed in the stroke direction of the piston, is arranged in each case as a roller guide in the spaces between the roller end sides and the cylinder inner surface, said wedge-shaped piece positioning the roller axially in the cylinder with respect to the lifting ring. The wedge-shaped pieces disclosed in the above-mentioned publication can essentially be divided into three different constructional types.
In a first type, each wedge-shaped piece has, on the side facing the roller, a planar surface bearing against the end side of the roller and, on the side facing away from the roller, a cylindrical surface in contact with the inner surface of the cylinder. In addition, this wedge-shaped piece is accommodated in the space between the roller, the piston and cylinder wall without being firmly connected to any of these components. Because the wedge-shaped piece is able to move freely in the piston direction with respect to the roller, the piston drives the wedge-shaped pieces in the direction of the lifting ring during a loading stroke. In the process, there is still no contact between the wedge-shaped pieces and the cams formed on the lifting ring. In contrast, during the subsequent return stroke of the piston the wedge-shaped pieces abut against the cams formed on the lifting ring and are pushed inward.
In a second constructional type, each of the two wedge-shaped pieces has, on the side facing the roller, a driver-like projection which extends between the piston and roller in the direction of the other wedge-shaped piece in a cutout provided on the piston. In this case, the wedge-shaped pieces are again driven by the roller into the cylinder during the return stroke of the piston.
In order to ensure the required rotational position of the piston and therefore of the rollers in the cylinder even if the rollers do not have any contact with the lifting ring, according to a third constructional type, one of the two wedge-shaped pieces has, on the side facing the cylinder wall, an elongated groove in which a locking bar in the form of a screw, clamp or the like, which is held on the cylinder wall, engages and thereby prevents torsion of the piston in the cylinder and therefore of the roller with respect to the lifting ring. An additional part is therefore required in order to torsionally secure the wedge-shaped piece and therefore the piston and roller with regard to the axis of the cylinder, and so the outlay on manufacturing is high.
The object of the invention is to develop a radial piston machine of the above-mentioned type in such a manner that it can be produced with a lower outlay with functionally reliable operation being ensured.
According to the invention, this object is achieved wherein at least one of the two roller guides of a roller is torsionally secured directly with respect to the cylinder block without an additional part. The outlay on production for the radial piston machine is therefore considerably reduced. This is because the manufacturing or the purchase, handling and the assembly of the locking bar engaging in the roller guide are rendered superfluous.
Thus, according to a feature of the invention a roller guide has a projection on its side facing away from the roller, while the cylinder is provided with a groove which runs in the axial direction and accommodates the projection of the roller guide in a form-locking manner in the direction of rotation about the axis of the cylinder. The roller guides are generally made of a plastic material, so that the projection on the roller guide can easily be worked from the solid or, if the roller guide is produced by injection molding, can be formed on it at the same time. After the working of the cylinder, a groove in the cylinder can be milled out If said groove advantageously extends inward from the open end of the cylinder, it may also be obtained by a small hole being initially made in the cylinder block and cutting being initiated there as a cylinder is being worked.
So that the roller guide is not subjected to pressure, according to another feature of the invention the groove in the cylinder extends inward until it is radially outside a point at which the lower side of the piston, which lower side faces away from the roller, is in its extended dead center. In particular, according to still another feature of the invention the position of the inner end of the groove, the position of a piston cup which is held on the piston and seals the gap between it and the cylinder, and the travel distance of the piston are matched to one another in such a manner that the piston cup does not reach into the region of the groove.
Advantageously, according to yet another feature of the invention the projection on the roller guide is a ridge which runs in the axial direction of the cylinder, so that a certain length is available for the form-locking engagement between the projection on the roller guide and the groove of the cylinder. The ridge on a roller guide is preferably situated in the center of the roller guide, as viewed in the axial direction of the cylinder, so that the roller guide is indifferent as regards the direction in which torsion of the piston and of the roller is prevented, and forces are introduced into the roller guide at its thickest point. In addition, during assembly the roller guide can be inserted into the intermediate space between the roller and the cylinder in two positions rotated by 180xc2x0 with respect to each other if the projection or the ridge lies symmetrically with respect to a plane running perpendicularly to the axis of the cylinder halfway up the roller guide.
According to still another feature of the invention, the contour of a groove of the cylinder, as viewed in the axial direction of the cylinder, is preferably formed by a circular arc because then the groove, as already indicated, can be worked in a particularly simple manner.
If both roller guides of a roller are torsionally secured with respect to the cylinder block, the forces required for the securing are divided over two roller guides, with the result that the projection or the ridge on the roller guides can be relatively low and the grooves in the cylinder can be relatively flat.